Game developers for years have tweaked the dials not only on how games look and sound but how they operate under the hood, and such changes have made videogames more pervasive and enthralling, industry observers say.

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Sony’s mobile role-playing game “Fate/Grand Order” takes up most of 31-year-old Daigo’s time—and a lot of his money: His in-game purchases total more than $70,000. It’s worth it, he says. Devotees like Daigo have made “Fate/Grand Order” Sony’s most profitable game ever.